Cardiac transplantation is the only curative therapy for patients with end-stage heart disease; however, there is a severe shortage of viable donor organs. Heart transplantation faces many interwoven challenges, including both biological factors and research limitations. For example, ischemia-reperfusion injury plays a role in early graft dysfunction and is associated with rejection episodes in heart transplantation. Moreover, experimental transplantation relies heavily on animal studies that are laborious and expensive, prohibiting the discovery of novel, bold solutions. We propose that the zebrafish,
Danio rerio
, would be a valuable tool for the field since it’s amenable to high-throughput screens, captures the complex structure of organs, and offers a suite of tools to monitor the biology of cardiac injury. Here, we develop a new subzero heart preservation method by strategically leveraging animal models from zebrafish to mammalian hearts. Using zebrafish larvae, we screened for agents which preserve hearts at -10°C. As a result of these screens, we identified promising preservative cocktails which restored heartbeat in 82% of larvae immediately post-recovery. Next, we excised adult zebrafish hearts and developed methods to mimic the
ex vivo
handling practices of hearts destined for transplant using a heart-on-a-plate assay. Using this assay, we carried forward promising agents identified in our initial zebrafish larvae screen to isolated adult zebrafish hearts that were cooled to -10°C and held for up to 24 hours. After rewarming, heart rate was restored and metabolic rate of zebrafish hearts was like time-matched controls (0.213 ± 0.047 and 0.275 ± 0.060, respectively, p = 0.200). Finally, we report our preliminary scale-up efforts whereby rodent hearts are stored for up to 24 hours at -10°C and viability were assessed by the TUNEL assay. The data shows high viability of cardiomyocytes post-preservation, as compared to controls. In summary, we present data to illustrate our efforts in leveraging the zebrafish to aid new discoveries in subzero heart preservation. Similar efforts to model heart transplantation in zebrafish may provide a different vantage point and enable us to make advances faster.
How to Save a Life: Ex Vivo Heart Preservation